Geminal Tetraauration of Acetonitrile: Hemilabile-Phosphine-Stabilized Au8Ag4 Cluster Compounds

Unprecedented geminal tetraauration of acetonitrile has been realized through C-H activation by Au(I)-Ag(I) clusters under mild conditions. The reaction of [OAu3Ag(dppy)(3)](BF4)(2) (dppy = diphenylphosphino-2-pyridine) (1), AgBF4, and acetonitrile in the presence of methanol at room temperature resulted in the isolation of the novel cluster [(CCN)(2)Au8Ag4(dppy)(8)(CH3CN)(2)]-(BF4)(6) (2). The centrosymmetric structure consists of two Au4Ag2 motifs stabilized by hemilabile phosphines. Triply deprotonated acetonitrile (CCN3-) is found in a Au4Ag environment with the terminal carbon bridging four Au(I) centers and the nitrogen donor, linking a Ag(I) ion, which is the first example of a mu(5)-CCN3- coordination mode. A concerted metalation/deprotonation process for the C-H activation of acetonitrile that indicates the importance of the oxo ion of the oxonium Au(I) cluster is proposed. Cluster 2 emits bright green light in the solid state at room temperature upon UV irradiation.